The birth of Jesus was the first step in the divine Son of God making himself lower and lower, before being raised up again and exalted in glory.
He has always existed, and always shared in the divine glory of his Father, and yet in the incarnation he chose to set aside the privileges of deity to live a fully human existence. Having lowered himself in this way, he did not choose to come as a powerful or privileged human, but as a servant, and then even submitted himself to the most humiliating death imaginable, the death on a cross.
Once Christ had humbled himself in this way, God the Father raised him from the dead and enthroned him in the position of honour and glory where all will bow before him and declare him Lord.
The self-humbling of Jesus that we see in this passage is a part of the Christmas story that gives us cause for worship and wonder, and it is also an example for us to live with the same kind of humility, putting the needs and desires of other before our own.